This invention relates to image projection displays and more particularly to systems and methods that utilize reflective imaging devices in combination with a dichroic cross-combiner assembly.
Projection systems have been used for many years to project motion pictures and still photographs onto screens for viewing. More recently, presentations using multimedia projection systems have become popular for conducting sales demonstrations, business meetings, and classroom instruction.
In a common operating mode, multimedia projection systems receive analog video signals from a personal computer (xe2x80x9cPCxe2x80x9d). The video signals may represent still, partial-, or full-motion display images of a type rendered by the PC. The analog video signals are typically converted in the projection system into digital video signals, and the signals are electronically conditioned and processed to control an image-forming device, such as a liquid crystal display (xe2x80x9cLCDxe2x80x9d) or a digital micromirror display device (xe2x80x9cMDDxe2x80x9d).
A popular type of multimedia projection system employs a broad spectrum light source and optical path components upstream and downstream of the image-forming device to project the image onto a display screen. An example of a MDD-based multimedia projector is the model LP420 manufactured by in Focus Systems, Inc., of Wilsonville, Oreg., the assignee of this application.
Significant effort has been invested into developing projectors producing bright, high-quality, color images that are also compact so that they can be portable. However, it is desirable to further decrease the size and weight of such projectors. Furthermore, conventional projectors, which use high pressure mercury arc lamps, have lamp lifetimes of roughly 2000 hours. It is desirable to use a light source with lifetime in excess of 10,000 hours so that the user need not worry about failure of the projector or the cost and effort of lamp replacement.
An alternative optical architecture is, therefore, desired that substantially decreases the size and weight of the projection system as compared with conventional projection systems and significantly enhances light source lifetime.
An object of this invention is, therefore, to provide a system and method for projecting an image that results in a decrease of size and weight and longer light source lifetime as compared with conventional technology.
Another object of the invention is to employ long life solid state light sources in a projector.
Yet another object is to employ reflective imaging devices in a projection display system to reflect light received from a light source to a projection lens via a cross-combiner assembly to provide a compact projection system.
Several embodiments of an image projection system are disclosed. Each embodiment includes a light source apparatus, three reflective imaging devices, a dichroic cross-combiner assembly, and a projection lens.
The light source apparatus is either three separate light sources that deliver blue, green, and red light or a polychromatic light source that delivers all three colors, each color preferably in a narrow wavelength band.
The blue, green, and red light is separately delivered to the respective reflective imaging devices. The reflective imaging devices are preferably MDDs, of which two different types are disclosed. Both micromirror displays have an array of quadrilateral mirrors that are pivotable, but one has mirrors that pivot on a diagonal axis and the other has mirrors that pivot on a longitudinally centered axis.
As indicated above, all of the embodiments utilize a dichroic cross-combiner assembly to combine the blue, green, and red light to form a composite image directed toward the projection lens. When the light source apparatus is three separate light sources that separately deliver narrow bands of blue, green, and red light, then the dichroic cross-combiner assembly is essentially a conventional X-cube that can operate with unpolarized light.
In other embodiments of this invention, the light source apparatus is a multicolor light source and the dichroic cross-combiner assembly has different configurations. The multicolor light source preferably produces narrow band spectra of blue, red, and green light. In a system that utilizes the multicolor light source with MDDs having mirrors that pivot on a longitudinally centered axis, the dichroic cross-combiner assembly has elongated rectangular sides that direct the light to the appropriate MDD and recombine the light after the displays reflect the light back into the dichroic cross-combiner assembly.
In a system that utilizes the multicolor light source with MDDs having mirrors that pivot on a diagonal axis, the dichroic cross-combiner assembly preferably includes two axially stacked X-cubes that are rotated slightly out of alignment. The bottom cube directs the light at an oblique angle to the appropriate MDD, and the top cube recombines the light after the MDDs reflect the light back into the top cube of the dichroic cross-combiner assembly.
A pair of optional lenses is preferably positioned in the optical pathway between the light source apparatus and the reflective imaging devices. The optional pair of lenses includes an anamorphic beam expanding lens and an anamorphic collimating lens. For a system with a light source apparatus that comprises three light sources there are preferably three pairs of these optional lenses. When the light source apparatus is a multicolor light source then only a single pair is needed which is positioned between the multicolor light source and the side of the dichroic cross-combiner assembly. Note that the light delivered from the light source apparatus arrives at each MDD at an oblique angle. This oblique angle is required to maintain separate paths of the light beams incident on, and reflected by, the MDD. Light reflected by xe2x80x9conxe2x80x9d pixels of the MDD is directed into the projection lens. The lenses between the light source and the MDD are configured such that it is uniformly illuminated, and illumination overfill is minimized.
It also preferably to employ an optional field lens between each MDD and the opposing side of the dichroic cross-combiner assembly to help direct the light in a focused configuration. Such field lenses enable the projection lens to be smaller because the light is delivered in a focused configuration.
The projection lens is preferably held in a frame that has a light-absorbing surface and that is positioned in a lens barrel. Use of a light absorbing surface in close proximity to the projection lens enables the pivotable mirrors of the MDDs to direct the light into the projection lens or, alternately, direct or xe2x80x9cdumpxe2x80x9d the light to the light absorbing surface.
Additional objects and advantages of this invention will be apparent from the following detailed description of a preferred embodiment thereof that proceeds with reference to the accompanying drawings.